a. Field of the Invention. This invention relates to apparatus for eliminating backlash in a gear system.
b. Prior art. Backlash occurs in a gear system because of necessary fabrication tolerances and is a function of the distance between the centers of two meshed gears. Some backlash is needed for clearance to accommodate lubricants, dirt and thermal expansion. Backlash in a gear system allows some lost motion when the driving gear slows or is reversed. In most applications, this lost motion does not present a problem. In some systems, however, such as in servo-controlled systems, gear backlash will result in instability of the driving system. The reason for this is that the driven gear is free to move without resistance through the backlash.
Antibacklash gears are known. Typically, an antibacklash gear is made up of two gears mounted adjacent to each other, with one of the gears being secured to a drive or driven shaft and the other being mounted for a limited movement on the first gear. A spring interconnects the two gears to urge the teeth of one gear out of register with the teeth of the other gear in such a manner that the out-of-register teeth of the two gears completely fill the space between two adjacent teeth on the gear with which the antibacklash gears are meshed. Generally, it has been the practice to so heavily preload the gears making up the antibacklash gear that the driving and driven teeth on the pair of meshed gears are never unseated. This heavy preload has the disadvantage that it will cause excessive tooth wear when heavy torque loads are transmitted.